Factors that affect the properties of magnesium phosphate cement

Magnesium phosphate cement (MPC) was prepared with dead burned magnesia oxide (MgO), potassium di-hydrogen phosphate (KH2PO4) and some retarders in a given proportion used in the same manner as Portland cement. Factors such as the w/c ratio, casting temperature and fly ash contents that affect the properties of MPC were studied in this paper. The experimental results demonstrate that the setting time was significantly affected by the w/c ratio and casting temperature. Adding fly ash can increase the setting time and flowability of fresh MPC paste. The compressive strengths of MPC paste prepared using various w/c ratios were measured at ages of 3 h, 1 d, 7 d and 28 d. The 3-, 7- and 28-day compressive strengths of MPC mortar prepared using various fly ash contents were also measured. The compressive strength of MPC paste decreased with an increasing w/c ratio, and the aged compressive strengths of MPC mortar increased with increasing fly ash content. The results also indicate that adding fly ash can improve the water resistance and dry shrinkage of MPC mortar. Finally, the hydrate products were analyzed using XRD and SEM.